Merge branch 'additional-semantic-testcases' into 'master'

Supplemental semantic test cases

See merge request !37

semantic/array_access_on_returned_value.java

+class Main {
+    public static void main(String[] arguments) {
+        Main main = new Main();
+        main.getArray()[0] = 1;
+
+        new Main().getArray()[0] = 2;
+    }
+
+    public int[] getArray() {
+        int[] result = new int[1];
+        result[0] = 42;
+        return result;
+    }
+}

semantic/assign_system.invalid.mj

+class Main {
+    public static void main(String[] arguments) {
+        System = null;
+    }
+}

semantic/assign_system_out.invalid.mj

+class Main {
+    public static void main(String[] arguments) {
+        System.out = null;
+    }
+}

semantic/field_access_from_static_context.invalid.mj

+class FieldAccessStatic {
+    public int nonStatic;
+
+    public static void main(String[] args) {
+        nonStatic = 42;
+    }
+}

semantic/field_access_on_class_identifier.invalid.mj

+class FieldAccess {
+    public int field;
+
+    public static void main(String[] args) {
+        new FieldAccess().accessField();
+    }
+
+    public void accessField() {
+        int i = FieldAccess.field;
+    }
+}

semantic/field_access_on_returned_value.mj

+class Main {
+    public static void main(String[] arguments) {
+        Main main = new Main();
+        main.getX().x = null;
+
+        new Main().getX().x = null;
+    }
+
+    public X getX() {
+        return new X();
+    }
+}
+
+class X {
+    public X x;
+}

semantic/system_shadowing.invalid.mj

+/*
+ * This should be rejected by a MiniJava compiler like it is by the
+ * Java compiler as the class "System" shadows the default System
+ * declaration, but cannot have a static field named "out".
+ */
+class System {
+    public static void main(String[] args) {
+        System.out.println(42);
+    }
+}

semantic/too_much_array_access.invalid.mj

+class TooMuchArrayAccess {
+    public static void main(String[] args) {
+        int[] array = new int[3];
+        array[2][1] = 42;
+    }
+}

semantic/unreachable_code.mj

+/*
+ * MiniJava compilers are not allowed to reject programs only because
+ * they contain unreachable code, unlike Java compilers.
+ */
+class UnreachableCode {
+    public static void main(String[] args) {
+        int i = 42;
+        return;
+        int j = 23;
+    }
+}